KRX3 the elecraft K3 Sub Receiver

My KRX3 arrived yesterday and after about 4 hours of work It was fitted into my K3. For those of you that don’t already know The KRX3 adds a second receiver of equal specification to the primary receiver to the K3

Generally sub receivers are useful to help find out where the dx station is listening in the pileup, to search for multipliers whilst ‘running’ in a contest or to monitor a second band.

The K3 with the KRX3 fitted has another ‘neat trick’ up it’s sleeve. If the KRX3 is configured with the same filters in at least some of the slots as the primary receiver it can be used for Dual antenna diversity reception. In this mode the Sub RX tracks the tuning of the main RX. I have been using diversity reception for a number of years for tropical band broadcast Dxing with my Racal RA-3702 however the K3 is the first amateur transceiver I have used that is actually capable of doing diversity reception well.

Icom’s Flagship 7800 fails miserably in diversity on two counts. Firstly the main and Sub RX have a small but constant frequency offset making it very tiring to listen to, secondly the tuning of the main and sub receivers cannot track.

On the Elecraft k3 tuning tracks both receivers (when linked) RIT also applies to both receivers making the k3 very easy to use in diversity mode.

Diversity holds a lot of promise for weak signal DXing where using 2 separate antennas can help reduce the impact of fading, QRM and noise

Diversity is also very useful for enhancing the ability to pull individual calls out of large pileups

K3 30M Diversity is a 5 minute audio clip of the K3 in Diversity mode. For a better idea of how useful this is listen with headphones on.

here is the YR2TOP beacon on a noisy 160m with K9AY loops on the left and a beverage on the Right
filter bandwidth is 150hz this time160m_beacon_k3

Here is a clip of an SSB pileup on 20m Here too diversity reception helps to separate the callersk3_20mssb_diversity

Those who bought two K3s for SO2R contesting can link the two together to provide diversity reception. I have briefly described my setup on the elecraft list and the LP-Pan list. Google {w4uk k3 diversity} for info.

Using 2 receivers tracked via software is not the same as diversity.
Each K3 uses it’s own internal frequency reference and as a result the two radios will always have at least a small frequency offset relative to each other. This offset destroys the stereo ‘image’ and renders diversity very much less effective.
The Icom IC-7800 has an offset between the main and Sub RX (due to DDS decimation errors I think?) and this renders the 7800 nearly useless for diversity reception

After to
have installed the sub receiver module in my K3 rx-tx, and as from the
owner’s manual
(on pag. 37), I try to set the sub receiver to a
different band from main, using “BSET” and
“BAND” buttons. So this set
don’t work, and on the display I read “MAIN”.
Before I set in the
CONFIG KRX3, the aux rf source on ANT-BNC.
Then in the CONFIG I try to
set to YES, the VFO IND: and again this set don’t work properly,
and on
the display I read “UNAVAIL”.
The MCU firmware uploaded is REV. 2.67 (
the latest regular release).
So where is the problem and how can I
solve it ?.

I too have the KRX3 and just love it, as your sound clips show it can be a very good tool. I have all the filters in both receivers matched (8 pole Inrad’s) and not only do I use it for diversity but also during contests to check out other bands to see if they are open or not. Also if a multiplier station very busy I leave the sub there and search and pounce with the main receiver.